Zofran (ondansetron) is a prescription medication classified as a 5-HT3 receptor antagonist, specifically developed for the management and prevention of nausea and vomiting. It is a cornerstone therapeutic agent in both oncology and postoperative care, renowned for its targeted mechanism of action and high efficacy profile. By selectively blocking serotonin receptors in the chemoreceptor trigger zone (CTZ) and the gastrointestinal tract, Zofran interrupts the neural pathways that initiate the emetic reflex. Its development represented a significant advancement in supportive care, markedly improving quality of life for patients undergoing emetogenic challenges. This product card provides a comprehensive, expert-level overview of its appropriate use, pharmacology, and clinical considerations.

Features

• Active Ingredient: Ondansetron hydrochloride.
• Drug Class: Selective 5-HT3 (serotonin) receptor antagonist.
• Available Formulations: Oral tablets (4mg, 8mg), orally disintegrating tablets (4mg, 8mg), oral solution (4mg/5mL), and injectable solution for intravenous or intramuscular administration (2mg/mL).
• Mechanism of Action: Potent and selective inhibition of serotonin 5-HT3 receptors, both centrally in the area postrema (CTZ) and peripherally on vagal nerve terminals in the GI tract.
• Onset of Action: Oral: approximately 30-60 minutes; IV: rapid onset, within minutes.
• Duration of Effect: Effects typically last for 4 to 8 hours following a single dose, depending on the indication and formulation.

Benefits

• Highly Effective Prophylaxis: Significantly reduces the incidence and severity of nausea and vomiting associated with highly emetogenic chemotherapy (HEC) and moderately emetogenic chemotherapy (MEC).
• Superior Postoperative Control: Proven efficacy in preventing and treating nausea and vomiting in the post-anesthesia care unit (PACU), facilitating smoother recovery.
• Improved Patient Compliance and Outcomes: By effectively managing debilitating emesis, it enables patients to complete full courses of chemotherapy, maintain hydration and nutritional status, and experience a better quality of life.
• Flexible Dosing Options: Multiple formulations allow for administration routes tailored to the patient’s condition, whether they are nil by mouth, have difficulty swallowing, or are in an outpatient setting.
• Favorable Safety Profile: Generally well-tolerated in most patient populations when used as directed, with a predictable side effect profile.

Common use

Zofran is indicated for the prevention of nausea and vomiting in several key clinical scenarios. Its primary use is in oncology for the prevention of acute and delayed chemotherapy-induced nausea and vomiting (CINV), often as part of a multi-drug antiemetic regimen that may include NK1 receptor antagonists and corticosteroids. It is equally critical in the surgical setting for the prevention and treatment of postoperative nausea and vomiting (PONV), particularly in patients identified as high-risk. While not a first-line treatment for general gastroenteritis, it may be used off-label in certain cases of severe nausea and vomiting, including hyperemesis gravidarum, though this requires careful risk-benefit evaluation and obstetrician supervision due to potential fetal risks.

Dosage and direction

Dosing is highly indication-specific and must be determined by a healthcare professional. For chemotherapy-induced nausea and vomiting, a common adult IV dose is 8mg or 0.15mg/kg administered 30 minutes before chemotherapy, followed by two additional doses 4 and 8 hours after the first dose. Oral dosing is typically 8mg twice daily. For postoperative nausea and vomiting, a single 4mg IV dose is common pre-induction or intraoperatively. Oral tablets should be swallowed whole with water, with or without food. Orally disintegrating tablets are placed on the tongue, where they dissolve rapidly without the need for water; the tablet should be handled with dry hands. Adherence to the prescribed schedule is crucial for prophylactic efficacy.

Precautions

Patients should inform their physician of their complete medical history, especially of recent abdominal surgery, constipation, intestinal obstruction, or electrolyte imbalances (e.g., hypokalemia, hypomagnesemia), as ondansetron may mask a progressive ileus. Use with caution in patients with congenital long QT syndrome, congestive heart failure, or bradyarrhythmias, as the drug may increase the risk of QT interval prolongation. Electrolyte abnormalities should be corrected prior to administration. Patients with phenylketonuria (PKU) should be advised that the orally disintegrating tablets contain aspartame. The injection formulation should not be mixed with alkaline solutions for IV infusion.

Contraindications

Zofran is contraindicated in patients with a known hypersensitivity to ondansetron or any component of the formulation. Concomitant use with apomorphine is contraindicated due to the risk of profound hypotension and loss of consciousness. The use of intravenous ondansetron is contraindicated for the prevention of nausea and vomiting associated with chemotherapy in pediatric patients due to the risk of over-exposure and subsequent QT prolongation; oral formulations may be used.

Possible side effect

The most commonly reported side effects are headache, constipation, and fatigue. A sensation of warmth or flushing may occur with IV administration. Less frequent but more serious adverse reactions require medical attention. These include:

• QT Prolongation: Dose-dependent prolongation of the QT interval on ECG, which can predispose to Torsades de Pointes, a potentially fatal arrhythmia.
• Serotonin Syndrome: Although rare, this can occur, particularly with concomitant use of other serotonergic drugs (e.g., SSRIs, SNRIs). Symptoms include agitation, hallucinations, tachycardia, hyperthermia, muscle rigidity, and autonomic instability.
• Hypersensitivity Reactions: Including anaphylaxis, bronchospasm, and shock.
• Extrapyramidal Reactions: Such as dystonia and oculogyric crisis, though less common than with older antiemetics like metoclopramide.
• Blurred Vision: Transient visual disturbances have been reported.

Drug interaction

Ondansetron is primarily metabolized by multiple hepatic cytochrome P450 enzymes (CYP1A2, CYP2D6, CYP3A4). Drugs that induce or inhibit these pathways may alter its plasma concentration.

• QT-Prolonging Agents: Concomitant use with other drugs known to prolong the QT interval (e.g., certain antiarrhythmics [amiodarone, sotalol], antibiotics [erythromycin, moxifloxacin], antipsychotics) may have additive effects and is not recommended unless deemed essential.
• Serotonergic Drugs: Combined use with SSRIs, SNRIs, MAOIs, tricyclic antidepressants, fentanyl, lithium, or tramadol may increase the risk of serotonin syndrome.
• Phenytoin, Carbamazepine, Rifampin: These CYP3A4 inducers may decrease ondansetron plasma levels, potentially reducing its efficacy.
• Tramadol: Ondansetron may reduce the analgesic efficacy of tramadol.
• Apomorphine: Contraindicated (see Contraindications).

Missed dose

If a dose is missed for prophylactic therapy (e.g., for CINV), it should be taken as soon as it is remembered. However, if it is almost time for the next scheduled dose, the missed dose should be skipped, and the regular dosing schedule resumed. Patients should not double the dose to make up for a missed one. For acute treatment of nausea, the dose can be taken when needed, adhering to the minimum time interval prescribed between doses (e.g., every 8 hours).

Overdose

Symptoms of overdose may be an exaggeration of known adverse effects, particularly visual disturbances, severe constipation, syncope, and dizziness. There is also a heightened risk of significant QT prolongation. There is no specific antidote for ondansetron overdose. Management consists of discontinuation of the drug and provision of supportive care, with close monitoring of the ECG and vital signs. Hemodialysis is not likely to be effective in enhancing elimination.

Storage

Store all formulations at room temperature (20°C to 25°C or 68°F to 77°F), away from light, moisture, and heat. Do not store in the bathroom. The oral solution should not be frozen. Keep the blister packs of orally disintegrating tablets sealed within the foil pouch until immediately before use. Keep all medications out of the reach of children and pets.

Disclaimer

This information is for educational and informational purposes only and does not constitute medical advice. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified health provider with any questions you may have regarding a medical condition or medication. Never disregard professional medical advice or delay in seeking it because of something you have read here. The author and publisher are not responsible for any specific health or allergy needs that may require medical supervision or for any adverse effects resulting from the use of information contained herein.

Reviews

• “As an oncologist, Zofran is an indispensable part of our antiemetic protocol. Its efficacy in preventing acute CINV allows our patients to tolerate their chemotherapy regimens with significantly less distress.”
• “In our PACU, IV Zofran is the first-line intervention for PONV. Its rapid onset and reliable effect have drastically reduced rescue antiemetic requirements and improved patient satisfaction scores postoperatively.”
• “While highly effective, we maintain a high index of vigilance for the potential of QT prolongation, especially in our elderly patients with polypharmacy. Appropriate patient selection and dose adjustment are paramount.”
• “The availability of the ODT formulation has been a game-changer for our pediatric and geriatric patients, as well as those who are too nauseated to swallow a pill. It ensures we can deliver effective therapy without the need for an IV.”